Production of silver sulfate grains using inorganic additives

Abstract

An aqueous precipitation process for the preparation of particles comprising primarily silver sulfate, comprising reacting an aqueous soluble silver salt and an aqueous soluble source of inorganic sulfate ion in an agitated precipitation reactor vessel and precipitating particles comprising primarily silver sulfate, wherein the reaction and precipitation are performed in the presence of an aqueous soluble inorganic additive compound containing a cation capable of forming a sulfate salt that is less soluble than silver sulfate or a halide anion or an oxyanion capable of forming a silver salt that is less soluble than silver sulfate, the amount of additive being a minor molar percentage, relative to the molar amount of silver sulfate precipitated, and effective to result in precipitation of particles comprising primarily silver sulfate having a mean grain-size of less than 70 micrometers.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]Reference is made to commonly assigned, concurrently-filed, copending U.S. Ser. No. 11 / 694,390 directed towards “Color Stabilized Antimicrobial Polymer Composites”, the disclosure of which is incorporated by reference herein.FIELD OF THE INVENTION[0002]The present invention relates to the production of silver sulfate particles produced by aqueous precipitation methods, and in particular micron sized silver sulfate particles produced with uniform size employing inorganic additives, and the use thereof as an antimicrobial and antiviral agent in polymeric materials.BACKGROUND OF THE INVENTION[0003]There are various uses for silver sulfate, including as a synthetic reagent; a source of silver in the preparation of catalysts, plastic composite materials and various platinum complexes; as well as a source of silver in some photographic processes. Recently silver sulfate has been incorporated into plastics and facial creams as an antimicrobial a...

AI Technical Summary

Benefits of technology

The present invention provides a process for producing micrometer-sized particles of silver sulfate with uniform morphology and size using aqueous precipitation methods. The process involves reacting an aqueous soluble silver salt and an aqueous soluble source of inorganic sulfate ion in an agitated precipitation reactor vessel and precipitating particles comprising primarily silver sulfate. An inorganic additive compound containing a cation capable of forming a sulfate salt that is less soluble than silver sulfate or a halide anion or an oxyanion capable of forming a silver salt that is less soluble than silver sulfate is added in a minor molar percentage to precipitate particles of silver sulfate with a mean grain-size of less than 70 micrometers. The precipitated particles are stabilized against excessive aggregation by the inorganic additive, resulting in less agglomerated aqueous dispersions and more readily dispersed dry or substantially dry powders of silver sulfate. The materials provided by the invention also often possess good thermal stability and impart antibacterial, antifungal and antiviral properties.

Problems solved by technology

In addition, with the miniaturization of the physical size of many objects and devices, a similar limitation on the physical size of material components is now commonly encountered.

Silver salts are widely known to be thermally and photolytically unstable, discoloring to form brown, gray or black products.

These reviews describe results that demonstrate that silver is effective as an antimicrobial agent towards a wide range of bacteria, and that silver can impact a cell through multiple biochemical pathways, making it difficult for a cell to develop resistance to silver.

However, the inclusion of substantial amounts of organic character in additives to silver sulfate materials has been shown to compromise the thermal stability.

For example, when compounded into melt-processed polymers such as polypropylene, an unacceptable degree of discoloration of the composites often results.

While considerable efficacy in destroying parasitic protozoa such as coccidiae and histomones resulted when these compounds were added to the drinking water of diseased chickens, turkeys and cattle, neutral silver salts of these kinds contain too much organic character for use in some applications.

This result is typical of polymer melt additives that either contain too much unstable organic character or are simply added in an excessive amount.

Despite various references to the proposed use of silver salts as antimicrobial agents in various fields as referenced above, there are limited descriptions with respect to approaches in the prior art for preparing silver salts, specifically silver sulfate, of sufficiently small grain-size and of optimal grain-size distribution as may be desired for particular applications.